This investigation should contribute to an improved understanding of periodontal disease by providing immunochemical information about cell surface antigens which may act as virulence-associated factors for Actinomyces viscosus T14V. This organism is associated with plague, root surface caries and the immunological sensitization of periodontal disease patients, and it also causes periodontal lesions in gnotobiotic rats. A mutant strain (T14AV) is avirulent for rodents and may lack virulence-associated antigen which is present in the virulent strain. The fibrillar antigens are being purified from cell wall extracts. They will be characterized by: approximate molecular weight, sugar and amino acid composition, immunodominant groups, and effects on lymphocytes. Homogeneous proteins (lectins and mouse myeloma proteins) will be screened to detect binding activities for the fibrillar antigens and other cell surface antigens from A. visosus T14V. Special effort is being made for the preparation of more specific antisera to each fibrillar antigen. These antisera will be used to identify which antigen(s) may be responsible for coaggregation with Streptococcus sanguis 34, and to search for differences between virulent T14V and the avirulent mutant, T12AV.